Ferrous poisoning of surface MnO2 during manganese greensand operation

Abstract

This study investigated the fundamental performance of manganese greensands for the removal of both dissolved manganese and iron species from solution. The hypothesis was that iron ions may detrimentally impact manganese removal and that the magnitude of this outcome was dependent upon greensand composition. Consequently, five greensand materials were examined in terms of repeatability of operation, the relationship of performance to physical criteria, the mechanism of removal, influence of solution pH and the performance changes that occur when manganese and iron were co-present in solution.All greensand medias were shown to remove Mn(II) over 5 treatment cycles, where the solid MnO2 media had a larger removal capacity (0.35mg/g) compared to the two coated medias (0.09 and 0.05mg/g, respectively). The greensand medias also showed a significant capacity reduction from 72 to 93% when Fe(II) containing solutions were examined. Fe(II) species were also found to leach considerable amounts of Mn(II) through reductive dissolution which negated the beneficial Mn(II) removal when treating solutions with co-present Fe(II) and Mn(II). Material characterization revealed that the Mn(II) removal mechanism did not involve any surface MnO2 phase change or rely solely on Mn(II) adsorption.